1. Field of the Invention
This invention is directed to a method and apparatus for recognizing document characters that have been scanned and digitized into dot patterns. More particularly, the present invention has applicability in any character recognition task, but is particularly useful in recognizing handwritten characters; for example, characters handwritten on bank checks.
2. Description of Prior Art:
Character recognition techniques in the past have matched characters against templates, or scanned key regions of characters, to look for key character features that would identify a character. These techniques work well as long as the character set being recognized is constrained to particular shapes or key features. As soon as the constraints are relaxed, as in the case of handwritten characters, template and key feature analysis of characters has a low probability of success.
One technique for dealing with handwritten characters is taught in U.S. Pat. No. 4,757,551 issued Jul. 12, 1988 to Kobayashi et al and entitled "Character Recognition Method and System Capable of Recognizing Slant Characters." The Kobayashi et al patent attempts to deal with handwritten characters by detecting the slant of character strokes and comparing character information to information stored in two different libraries of characters that differ based on the slant of the reference characters in the library. Kobayashi uses directionality codes for character contour pels. The directionality codes simply indicate the direction from a given character pel to its next adjacent pels in the character. A histogram of these directionality codes is taken for sections of the character and matched against a library of histograms of reference character features to recognize the character.
One difficulty with Kobayashi's technique is that it is basically a template matching technique and requires large numbers of templates (reference histograms) against which the character feature histograms must be matched. Thus, the technique requires large amounts of storage and is time consuming to execute.